This invention relates to improvements in an organic polymeric material which exhibits a high sensitivity and a high contrast characteristic to radiations such as electron beams, ion beams, .gamma.-rays, neutron beams and X-rays. More particularly, it relates to a novel composition free from instability.
The term "instability" is intended to mean the insolubility (spontaneous insolubilization) of unirradiated parts of the polymeric material.
As is well known, electron beam-sensitive organic polymers are noticed as materials to replace photosensitive resins and are being put into practical use as, for example, resist materials. The resist materials are broadly classified into a photo resist exploiting photosensitivity, and an electron-beam resist exploiting electron-beam sensitivity. A deep-UV resist, an X-ray resist or the electron-beam resist is noticed in that a precision working is possible.
Some of the inventors have previously proposed as a material of this type a radiation-sensitive material which comprises a polymeric material having a plurality of epoxy groups and a plurality of bromine atoms in one molecule thereof (Japanese Patent Application No. 51-16029, corresponding U.S. Patent Application Ser. No. 768,728 filed on Feb. 15, 1977).
This radiation-sensitive material is made of at least one polymeric material selected from the group consisting of brominated and epoxidized polymers of butadiene, brominated and epoxidized copolymers of butadiene, brominated and epoxidized polymers of isoprene, brominated and epoxidized copolymers of isoprene, brominated products of copolymers of butadiene with addition-polymerizable compounds containing an epoxy group, brominated products of copolymers of isoprene with addition-polymerizable compounds containing an epoxy group and epoxidized products of copolymers of one of butadiene and isoprene with addition-polymerizable compounds containing a bromine atom.
The polymeric materials can be produced by subjecting a polymer or copolymer containing a plurality of carbon-to-carbon double bonds in one molecule, such as polybutadiene, polyisoprene, a butadiene copolymer or an isoprene copolymer, to addition of bromine and epoxidation in succession or simultaneously, or by subjecting a copolymer of a diene compound with an epoxy group-containing, addition-polymerizable monomer to bromination. The procedures for producing these polymeric materials, as well as the characteristics of these materials, are described in greater detail in the heretofore mentioned application Ser. No. 768,728, the disclosure of which is incorporated by reference.
The polymeric materials have high sensitivity, high resolution and high contrast characteristics as the radiation-sensitive materials. Owing to the high sensitivity, they are useful as recording materials in the field of recording information.
An example of the case of employing the radiation-sensitive materials as electron-beam resists will be explained with reference to FIGS. 1-A to 1-C.
As shown in FIG. 1-A, a metallic evaporated film 2 is formed on a glass substrate 1, and a coating film 3 of the radiation-sensitive material is formed thereon by applying a resist solution containing the radiation-sensitive material and an appropriate solvent. A part of the coating film 3 is irradiated by an electron beam 4 in a suitable dose, whereupon the coating film is treated with a proper organic solvent (liquid developer). Then, that part of the coating film which has not been subjected to the irradiation by the electron beam is dissolved and removed, and only that part of the coating film which has insolubilized owing to the irradiation by the electron beam remains without being dissolved in the solvent, so that a state illustrated in FIG. 1-B is attained. The structure in this state is further treated with chemicals which etch the metallic evaporated film 2, thereby to obtain a structure in a state shown in FIG. 1-C wherein only the metallic evaporated film in an area corresponding to the remaining part of the coating film 3 is left and wherein the metallic evaporated film in the other area is dissolved and removed. In this way, a glass plate in which the metallic evaporated film remains only in the area irradiated by the electron beam can be obtained. If, in the irradiation by the electron beam, a certain pattern is depicted on the polymer coating film with the electron beam, the metallic evaporated film will remain according to the depicted pattern on the glass substrate after the step of etching the metallic evaporated film. Using an electron-beam depicting equipment and the electron-beam resist in this manner, even a complicated and very fine pattern can be worked extremely precisely, and a metallic evaporated film of any desired design can be obtained. When a sample and a mask are held in close contact and they are irradiated by electromagnetic waves of short wavelengths, e.g. X-rays, a complicated and very fine pattern can be worked extremely precisely and a metallic evaporated film of any desired design can be obtained likewise to the above.
It has been revealed, however, that when the polymeric material containing epoxy groups and bromine atoms that has been let to stand after the synthesis is applied in conformity with the steps of FIGS. 1-A to 1-C, a phenomenon in which the width of a line irradiated by an electron beam becomes somewhat greater can take place. It has also been revealed that the resist solution undergoes insolubilization little by little also when let to stand, that the viscosity and sensitivity of the resist solution rise with the insolubilization, and that when the insolubilization becomes more conspicuous, a phenomenon in which the entire solution solidifies can take place.
That is, in case where, by way of example, a structure in the state of FIG. 1-B is to be obtained by irradiating the desired part of the coating film 3 in FIG. 1-A with the electron beam and thereafter conducting the developing treatment with the organic solvent, the sensitivity can become different depending on the date of irradiation, the degree of fog and, accordingly, the width of a line can become different depending on the developing period of time, or a fog film can appear in an unirradiated area. Such fogging phenomena give rise to the instability of the operations, and become a very serious problem in the technological field of semiconductor devices requiring precise working, especially in the field of integrated circuits (IC's), magnetic bubble domain memories, etc. requiring high working precisions in complicated microcircuits. A method for preventing such fogging phenomena must be taken by all means.
The phenomenon in which the organic polymer coating film in the unirradiated area or the resist solution becomes insoluble, as described above, is usually called the "spontaneous insolubilization" or "instability". Although the mechanism by which the phenomenon is caused is not clear, the most important cause will be that the polymeric material being the resist material is dissolved little by little, induces cross linkage in any form and consequently affects the fog.